At present very little is known about language development in prelinguistic infants and young children. However, research has demonstrated that infants do learn about their language over the first several months ,particularly in terms of the language's sound structure. The first goal of the research proposed here is to assess what elements of language are learned by infants using general psychological learning mechanisms capitalizing on the speech infants hear around them. This will be done through computational modeling of corpora of speech to young children, and through perceptual experiments with infants. The second goal of the research is to create a procedure capable of assessing individual children's development of accurate memory for words. This procedure will then be used to investigate possible sources of variation between children in word learning, word representation, and efficiency in understanding speech. Longitudinal studies of one-year-old infants will examine the development of adult like forms of words, and why individual infants may differ in early language learning.